Control for electric furnaces



Nov. 29,1927. 1,650,624

E. C. GLITZKE CONTROL FOR ELECTRIC FURNACES Filed NOV. 19. 1926 l-ZZAIQSAE: CITY, IVIZS COIZTTRUL ELECTRIC FU'EE'IACES.

Application filed November This invcution relates to improvements in ic furnaces, and rotors more particw j to the method of cont olling and. rogulatiug the furnace temper L within the vures in file of an electric rurnace.

e impor ant objects of the ini e a fusible wire inter- 't supplying current to the or or resistance wire heating coil which i tone at a predetermined temperature 3 on as the temperature desired for the 1. or treatment of material contained e :lurnace.

invention is described in connection nail dental electric furnace in which porcelain is fused in the making ot' artificial teeth. but it will he understood that the invention is applicable to any type oi? laborat or commercial electric furnace c ctric power is utilized as the means the furnace.

1S a :rront elevational View of a rurnace.

is a side VlSW with a portion l3 lJlOliED away, showing the muffle and positioning; of the fuse wire.

3 is an inside View of the muiiie door.

Fig. 4 is a diagrammatic view ot the electric circuit.

lteferrinp' to the drawings at 1 is shown an electric iurnace for dental use. 'llhis furnace is mounted upon any type of suitable standz'ard 2. The furnace consists of a. cylinder of highly refractory ceramic material shown at 3 in the cut-away portion in Fig. 2. This insulating material is surrounded by a metal jacket. The muffle 4 is a small hollowed-out chamber in the ceramic mate rial. lmbedded in the top of the muffle is a wire 5 shown in 2 and Fig. 'lhetront ot the mu'lile is closed by means of a muffle door 6 upon which are mounted the binding posts 7 and 8.

@n the standard of the furnace is a variable resistance rheostat having; contacting buttons 9 which are engaged by means of a lever 10 in order to increase the current supplied to the resistance coil or resistor element within the muffle chamber and by means oi which the furnace is heated. The

19, 1925. Serial No. 149,323.

source of current or power is supplied through the power lines designated as ll. and which are connected to the binding posts 13 and I l of a switch. The arm 15 oi the switch is pivoted on the binding post Ilel and may be thrown to engagement with the hi. ding post 13 or to a second binding post 16 which has connection throu 'h a line 17 with the resistance coil in the turnace. The binding post 13 is connected by a wire 18 upon the binding post "I on the muffle door and the lever of the rheostat 10 is connected by a line 19 to the binding post 8 on the muiile door while the contacting buttons of the rheostat have connection through a line 20 to the resistance wire or resistor in the furnace.

It is usual practice in the heating of naces by electricity to have positioned with in the muii'le a thermocouple which is connected to a registering pyrometer in order that the operator can ascertain the mutlie temperatures. The thermocouple and Pf.- rometer arrangement has been. and is. unsatisfactory where an accurate temperature is desired and particularly at high temperatures, variations of considerable rac s are experienced, occasion by the fact that atthese high tempera-ti: es the record! 9' pvroineter is less sensitive. Variations in the current will also produce irregularities which are more or less disasaitrmis to the maintenance of accurate mullle tcmperatures, variations being troublesome in the fusion. or heating of material, such as porcelain, where accurate temperatures are es sential to produce the desired hardness and coloring in dental work.

Under certain conditions, it is also essential to bring a material gradually-up to temperature and immediately discontinue heating when the temperature has arrived at a particular point which it is desirable to accurately ascertain.

Experience with recording pyrometers has been so unsatisfactory that the present method of controlling these temperatures has been resorted to. In place of a pyror'neter, a fusible wire 21 is connected to the binding posts 7 and 8 mounted upon the muti'le door and extends in a loop through holes in the door into the furnace muffle. A metal or an alloy of metals selected which has a fusion temperature at the desired temperature which is to be reached in the mutl'le and the switch 15 is thrown into engagement with the binding post 16 so that the power is supplied to the heating coil,the circuit being completed by means of the switch and fusible wire connecting the binding posts 7 and 8 on the mulile door. These binding posts are connected to the binding post 13 and the rheostat, respectively. The temperature is ,g 'radually raised. in the mullle by advancing the lever 10 successively through the range of the rheostat, across the contacting buttons, and lhcrchg. llltl't ,inp; the heat supplied to the lnutl'le. Within the niullle is placed porcelain or other material to be treated, designated as 22 in Fig. 2. upon a removable slab 23 of refractory n'iaterial. lVhcn. the temperature in the muffle has reached the fusible temperature of the wire 21, the wire melted and the circuit broken.

.ln this manner, the temperature to which the turns-cc n'iu'i'lle is raiz-4ed may be accurately determined and controlled.

Below are enumerated a number of metal combinations which have been used for the regulatioi'i of furnace temperatures and with which. satisfactory results have been obtained. Also, a list of metals have been selected which would fuse at somewhat lower temperatures if s ch temperatures were desirable for purposes other than the fusion or treat nent of porcelain.

AZZQQ/S limit Hg melting poi m5 0] 2300 F. (ZQGO 0.)

Per cent. Per cent.

Copper 90'Cobalt 10 Nickel l3---UO1)1J(-EI 31" l-lickel rrrrrrrr TS-'l.inr Nickel lQ-Jlead--. i .....-,i (8

Manganese. ltltl-- i. t opper i. 5'-l- Silicon f; 4-6 (wiper Sik -Tron ll] /l/70!/ hum'n melting point 07' @500 F.

Zl/cZtiwg points 0/ Ii/(211118,

Centigrade.

One dental supply company at the present time furishes porcelain identified as low fusing, medium. fusing and high fusing,thc first IiillHll'l Q at approximately 1700 F the second at 23W) and the latter at 2441) ll.

By the use of a fu ible wire of one of the selected alloys, the temperature of the mid le is maintained. r 'thin a selected range and there is no possibility of overheating.

This control also permits the functioning of the furi'iace while other work is being donc,a practice which is not permitted where the operator must rely upon pyroineter control.

As suggested, although the invention has been de cribed in connection with dental work, it will. be recognized that it is as adaptable to any type of furnace in which electricity is used for heating.

A number of metals or alloys of n'ietals have been herein, suggigested, but this by no means exhausts the possibility of fusible substances adapted for such use.

I claim as my invention:

1. An electric furnace control for limiting normal furnace ten'iperature con'mrismu a furnace having; a heating element therein, said heating element connected in. an ele tric circuit, a closure for said furnace, binding posts, mounted on said closure and interposed in the electric circuit, a fusible element having a predetermined nu-ilting point, connecting the binding: posts a nd ct'nnpl-ctilui; the circuit, and extending into the furnace to receive the san'ie heat. as the material undergoing treatment.

An electric fin'nace control for limiting normal furnace temperatures, comprising a furnace having a heating element therein said heating element connected in an electric circuit, a removable closure for said furnace and connections interposed in the circuit mounted on said closure, an element fusible at a predetern'iined temperature between said connections con'ipleting the circuit and extending through the closure into the furnace to receive the direct radiated heat thereof.

' EVVALD C. GLITZKE.

ill)

ltlii 

